Opposed Twin I.C.

[Brian Rupnow]

Jason--You're right, and that is a great idea---as long as the cylinders are in line with each other. Unfortunately, with them offset as shown, it won't work. I have found that by using a 36 tooth and an 18 tooth gear, I can avoid having to cut a jockey gear to fit between them since I don't have the same physical constraints as the original engine. I have to do a bit more modeling to decide whether I like them, or if they will look too big and "clunky".

[Dave Otto]

Brian, I think Gade also made an opposed twin, basically two aircooled hit and miss cylinders much the same as my Recent Gade build but on opposite ends of the main bed casting. Just need to find the photo I saw of it (as a model)

The other option would be to say your engine is a 180degree Vee twin and then you can use a single crank pin

Hi Jason

Look on Roland and Marvin's site http://www.morrisonandmarvin.com/gade_12hp.php

Dave

[Dave Otto]

Jason--You're right, and that is a great idea---as long as the cylinders are in line with each other. Unfortunately, with them offset as shown, it won't work. I have found that by using a 36 tooth and an 18 tooth gear, I can avoid having to cut a jockey gear to fit between them since I don't have the same physical constraints as the original engine. I have to do a bit more modeling to decide whether I like them, or if they will look too big and "clunky".

I don't understand; VWs have offset cylinders and use only one camshaft centered under the crank?

[Brian Rupnow]

Don't ask me what I'm doing----I'm not sure myself!! Just messing about, modeling, figuring out how I'm going to do this. Right now it's looking like two pieces of aluminum angle, right and left hand bolted together to form the main body, but that may change.

[Brian Rupnow]

Dave--I could do the same as VW if I squeezed all four cams onto one shaft and changed the offset of the valves in the cylinder head. However, since I have to cut the gears anyways, it's easier for me to just cut the gears a bit longer and part two off the same stock and arrange things with two separate cams.----Brian

[gbritnell]

One issue that hasn't been discussed is how you're going to lubricate both the rods and cams. For the cam followers you could make roller tappets but for the rods I don't know. With an open crankcase you're going to have oil flinging about when the engine is running.
gbritnell

[Dave Otto]

The valves on an air cooled VW are symmetrical to the cylinder; the push rods are at a slight angle.

Dave

[rklopp]

The Upshur Twin has a single camshaft with two wide lobes. Each lobe has two tappets riding on it, from opposite sides. The pushrods are angled fore and aft laterally a little bit.

[gmac]

rklopp beat me to it......as shown here;

http://www.floridaame.org/GalleryPages/g1M0294.htm

Cheers Garry

[Jasonb]

Brian mine has a single cam shaft, no changes to the head, all I did was put the two cental cams slightly closer together

[Jasonb]

I don't understand; VWs have offset cylinders and use only one camshaft centered under the crank?

Brian as you were asking about hopper cooled twins, why not turn the whole engine upside down with the camshaft below the crank. Then instead of the aircooled cylinders you could do the watercooled ones but rather than turn from round stock make them from block with a "U" shaped section to form two small hoppers



You could also stretch out the central "box" and have slightly longer cranks which would also give the old style look to the engine.

[Brian Rupnow]

Damn Jason!!!---your brain works at the same speed as mine at "imagineering". I certainly like all of your ideas.--Don't you mean slightly longer con rods?---Brian

[Jasonb]

Yes Conrods. Though having just seen the engine Dave has posted in the two cylinder Horz thread I'm not so sure its needed

[Brian Rupnow]

This is one of those rather unusual cases where, after massive amounts of cutting and carving and rearranging, everything seems to work just fine by bolting two pieces of 1/2" thick aluminum angle together toe to toe. Everything fits, clears, and seems to look surprisingly good. I did lengthen the connecting rods by 1/4" thereby moving the cylinders out 1/4" more from the center-line of the crankshaft to give myself a bit more room. I will make gear covers---Not so much as a safety factor, but as a noise dampner. Those meshing spur gears make a heck of a racket. It would be nice to machine the gear covers from clear Lexan so the gears remain visible but the racket is kept quieter. It appears that the two angles can be machined to finished size, bolted together and dowelled, then drilled and reamed thru both sides in one set-up for oilite bronze bushings for the crankshaft and both camshafts. The angles could then be unbolted to install the crankshaft and camshafts, then reassembled.

[cfellows]

Just a heads-up while you are talking about camshafts... have you thought about the ignition?  If you plan to use a distributor, you will probably want to run it off your camshaft.  Or, with a twin, you could get by with waste-fire, just firing both cylinders at the same time on every revolution of the crankshaft.

Chuck